Removed navbar from PAPasscodeViewController to make iOS 7 compatibility easier

* iOS 7 navbar height logic is a little complex because of the way it
* determines and handles underlapping the status bar.

* It's probably best to leave this behavior up to iOS rather than
* trying to re-implement it here, so I removed it

* To show a navbar at the top the way it was before, simply present
* PAPasscodeViewcontroller inside of a UINavigationController